Modem blade sharpeners depend upon precise control of the sharpening angles in order to obtain the sharpest knives. Generally there are precision guides which insure that the blade is held at the same angle relative to the plane of the sharpening abrasive or to the plane of the sharpening steel on each and every sharpening stroke. In order to develop the sharpest edges it is important that the blade and the surface of the abrasive material be held in a consistent angular position on each sharpening stroke across the abrasive.
In order to maintain a consistent angle of the facets (that meet to create the edge) as they contact a sharpening or steeling element, it has been shown important to have angle guides that physically relate to some feature of the knife blade. It is convenient and practical to reference from the face of the blade to set the angle of the blade edge facets relative to the surface plane of the sharpening or steeling element at the point of contact.
Consequently it is common in sharpening to lay the face of the blade against a planar single guiding surface and to slide the blade with its face in good physical contact with that surface while the edge facet is being modified by the abrasive or steeling element.
Physical guides using the face of the blade being sharpened as the reference to set the angle of the blade facets to the abrasive can be extremely precise because of the generally large and flat structure of the face of most knives. However, because the blade face must be held in relatively firm contact with the flat planar surface it is necessary to keep that surface clean of foreign materials such as swarf and abrasive fragments in order to avoid some scratching or burnishing the blade face. Because blade faces are commonly polished at the factory in a direction perpendicular to the edge, even mild abrasive action parallel to the edge can in time cause a mild burnishing along the blade face. This is not a functional problem that interferes with obtaining a sharp edge, but it is a cosmetic issue for knife collectors who purchase expensive knives. It is therefore desirable to seek improved means to eliminate this effect.
Means of reducing this scratching and burnishing effect have been described previously and patented by this inventor. These include the use of multiple rollers as disclosed in U.S. Pat. Nos. 5,406,679 and 5,449,315, guiding against vertical guide surfaces with or without rollers in U.S. Pat. Nos. 5,390,431 and 5,582,535; plastic surfaced rollers in U.S. Pat. Nos. 5,449,315 and 5,404,679; guide planes created by a number of ball bearings and moving a guided sharpener along the blade edge U.S. Pat. No. 5,582,535.
While most of the previously disclosed means of reducing random scratching or burnishing of the face of knives as they are moved along physical guides have proven useful they have not completely eliminated the scratching and burnishing. As a result research was initiated to develop improved approaches and alternative solutions that will virtually eliminate these undesirable effects for extended periods of time.